This is example #248 of why I never get why people think Amazon's customer service is so good. I find it no better than any other at best, and frequently infuriating.
Long story short: When I tried to buy an Echo Dot under the trade-in program, I got the gift card amount applied to my total, but I did not get the 25% discount. A frustrating conversation with customer service which included my walking them through my invoice more than once, several instances of dead time, and being booted to someone higher up, eventually (35 minutes later!) to acknowledge that indeed, I had not gotten the discount I was entitled to. And, that they'd issue a promotional credit to my account for the difference.
That was way too big an investment of my time when Amazon's website wasn't up to handling Black Friday promotions. And while I got them to up the credit to $10, I never buy from Amazon any more. it'll get used eventually, but it's going to sit some time. Breakage goes to the business, alas.